In recent years, comprehensive engine control based on the use of a micro-computer has been increasingly adopted with a view to enhancing control functions for engine operations.
As is well known in the control of motor vehicles, the control functions required for controlling the engine operations will vary in dependence on the types of the motor vehicles as well as the purposes which are to be accomplished with the applied control. Under the circumstances, there is a great demand, in view of the need for economy and enchanced controllability, for such a microcomputer-based engine control system which allows common software to be employed for activating the engine control system independently of the types of the motor vehicles and applications which the control system is to serve and, in addition, which allows the control function to be modified, altered or even additionally corrected in accordance with alterations of the motor vehicle and control purpose.
Heretofore, the quantity of suction or intake air fed to the engine has been in most cases, detected by using a hot-wire type air flow sensor in view the relative inexpensiveness thereof. In this connection, it has to be noted that the intake air flow does not remain constant but undergoes pulsating variations. Further, the output signal available from the hot-wire type air flow sensor has a non-liniear relation to the actual quantity of suction air flow, in addition to the fact that the air flow sensor exhibits a rapid response or high sensitivity to variations in the intake air flow. As a consequence, the output signal from the hot-wire type air flow sensor does not necessarily represent the actually drawn in air quantity with an acceptable accuracy. It should further be pointed out that the software design is, as a whole, very complicated and difficulties have heretofore been encountered in modifying the software in dependence on the types of motor vehicles and/or in accordance with alterations in applications.